Wireless telecommunication systems are well known in the art. In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS and EDGE are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute-Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.
A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), known as User Equipments (UEs) in 3GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs are connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.
Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station's timing. In 3GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator's networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers. The gateway mobile services also receives and administers connection requests from subscribers from external networks.
The RNCs generally control internal functions of the UTRAN. The RNCs also provides intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS.
Typically a RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection.
Various methods of power control for wireless communication systems are well known in the art. Examples of open and closed loop power control transmitter systems for wireless communication systems are illustrated in FIGS. 2 and 3, respectively. The purpose of such systems is to rapidly vary transmitter power in the presence of a fading propagation channel and time-varying interference to minimize transmitter power while insuring that data is received at the remote end with acceptable quality.
In communication systems such as Third Generation Partnership Project (3GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems, multiple shared and dedicated channels of variable rate data are combined for transmission. Background specification data for such systems are found at 3GPP TS 25.223 v3.3.0, 3GPP TS 25.222 v3.2.0, 3GPP TS 25.224 v3.6 and Volume 3 specifications of Air-Interface for 3G Multiple System Version 1.0, Revision 1.0 by the Association of Radio Industries Businesses (ARIB). A fast method and system of power control adaptation for data rate changes resulting in more optimal performance is taught in International Publication Number WO 02/09311 A2, published 31 Jan. 2002 and corresponding U.S. patent application Ser. No. 09/904,001, filed Jul. 12, 2001 owned by the assignee of the present invention.
Where shared channels are utilized, different WTRUs can use the same channel and channel use by a particular WTRU can be sporadic. The inventors have recognized that the metric used for adjusting power control in the conventional manner for a specific shared channel may not be readily available since the relative position of the WTRU may have substantially changed from when it last used the specific shared channel. Accordingly, it is desirable to provide method and apparatus for controlling the power of shared channels where there may be sporadic use of such channels by WTRUs.
For example, the physical channels specified in 3GPP Release 5 (R5) of UMTS Terrestrial Radio Access Time Division Duplex (UTRA TDD) include a High Speed Shared Information Channel (HS-SICH) which operates in conjunction with a High Speed Downlink Shared Channel (HS-DSCH). HS-SICH is a fast Uplink (UL) feedback channel used in UTRA TDD R5 for High Speed Down link Packet Access HSDPA operation. The HS-SICH carries a 1-bit Ack/Nack message and a several bit long measurement report from a particular WTRU that received a downlink (DL) transmission on the HS-DSCH.
The HS-DSCH is an HSDPA R5 DL channel used to send packages at very high throughput to users that use scheduling based upon estimated instantaneous channel quality for different users and fast Level 1 (L1) retransmission techniques including hybrid automatic repeat requests (ARQ). Only a single WTRU receives a DL transmission on a HS-DSCH in any given Transmission Time Interval (TTI) which is currently specified as 10 ms for the HS-DSCH. The particular WTRU that receives the transmission acknowledges successful/unsuccessful reception of the DL transmission on the HS-SICH within a specified TTI such that there is a 1:1 correlation between TTIs containing a DL HS-DSCH for a particular WTRU and the TTI containing the WTRU's UL acknowledgement. Preferably, the acknowledgment is sent in the ith TTI following the DL transmission TTI, where i is fixed and greater than 5. Thus in a given TTI, only one WTRU transmits in the UL HS-SICH, but different WTRUs use the UL HS-SICH for acknowledging packet reception in other TTIs, respectively.
As with other UL channels, it is desirable to use a loop type power control by a WTRU for determining the necessary UL transmission power for the HS-SICH. Conventionally, the WTRU can be configured with an open-loop power controlled transmitter as shown in FIG. 2 where the WTRU measures DL path loss and takes into account UL interference levels broadcast or signaled from UTRAN to the WTRUs.
In order to meet certain quality reception targets, a so-called outer loop power control is also preferably implemented in the open loop power control as shown in FIG. 2 where a Tx power adjustment is made in response to a metric such as a target Signal to Interference Ratio (SIR). The target SIR is used to control the reception quality of the signal. A higher target SIR implies better demodulation, but more interference created by other users in the system. A lower target SIR implies lower interference created for other users in the system, but the demodulation quality is lower. Conventionally, the target SIR is dynamically adjusted by the outer loop power control that updates the desired value as a function of interference in the system and quality of the UL channel.
Outer-loop functionality for a WTRU relies on observations of received UL transmissions by a base station such as observing block-error rates (BLER) or received SIRs. If for example the BLER becomes higher than allowed, such as BLER>0.1 in 3GPP R5, and the user data becomes unusable because of too many errors, a higher target SIR is signaled to the WTRU that the WTRU in turn will apply to adjust its transmit power. However, the time-shared nature of shared channels such as the HS-SICH where a particular WTRU only transmits in the channel sporadically makes it very difficult to observe WTRU specific BLER or measured SIR with a frequency to assure consistent outer loop power control.
To ensure system operation and for simplicity, a high target SIR on HS-SICH accommodating the worst case WTRU with the worst case target SIR can be chosen in place of outer loop power control where measurement is made of received UL signals from the particular WTRU. However, the resulting degree of interference makes it difficult to allocate other channels into a Time Slot (TS) containing the HS-SICH. Consequently, resources are wasted. The fact that it is desirable to operate several channels in a TS containing HS-SICH, for resource efficiency, aggravates this problem. Without outer loop power control, code resources in a HS-SICH timeslot are wasted. Generally, if WTRUs cannot achieve reliable UL Tx power on HS-SICH in large cell portions, HSDPA operation in UTRA TDD may be heavily compromised. Thus, it is desirable to provide a mechanism for UTRA TDD that allows accurate updates of WTRU specific target SIR values for HS-SICH operation.